Finite element simulation of reactive flow in the active area of an SOFC stack

A 3D-Finite Element Analysis of the electrochemically active area of a SOFC Stack is presented. The model is focused on the fluid dynamics coupled with thermal balances and electrochemical reactions over a three dimensional homogenized geometrical structure. Based on the equations of fluid flow through porous media a generalized formulation of the mass and momentum transport processes was implemented. It allows a flexible simulation of more complex flowfield designs as for instance the fuel gas flow through a foam layer. The computations rely on a C++ source code program developed within the commercial finite element code library DiffPack. The mathematical solution could be stabilized and optimized as the programming environment of DiffPack permits the implementation of numerical schemes differing from standard Finite Element (FE) methods. The transport equations are treated by a non-standard Least-Squares FE approach. An example for the application of the simulation for different stack designs is presented. The effect of inhomogeneous fuel distribution within the active stack area with respect to stack power and stability of the stack operation is studied for several design variants. It could be demonstrated that the effect of the inhomogeneous gas distribution on the global stack characteristic remains negligible in the range of low to intermediate fuel consumption but sets a limit to safe stack operation in the case of high fuel utilization. A different anode flowfield design, allowing an exchange between the differently exhausted gas regions, results in a more homogeneous field distribution and extends the range of stable stack operation to higher fuel utilizations. The model conclusions have been confirmed by comparison with experimental results